Proteases and Chitinases Induced in Beauveria bassiana during Infection by Zabrotes subfasciatus

The Mexican bean weevil, Zabrotes subfasciatus (Boheman), is a major insect pest widely distributed in northwestern Mexico. The pest affects the common bean postharvest, causing losses of 25-40%. One alternative to synthetic insecticide for controlling the pest is use of Beauveria bassiana (Bats.), which by secreting hydrolytic enzymes is able to infect adults of Z. subfasciatus. In this study, strain B. bassiana code B02 with greatest pathogenicity was selected from 10 native strains. Proteolytic and chitinolytic activity were measured to determine the enzymes involved during the infection process. All strains showed pathogenicity, killing 100-70% of the insects with TL50 of 1.3-3.7 days. No adults emerged when insects were treated with strain B02 because of the effect of proteases and chitinases. Subsequently, the proteins induced during infection were analyzed by SDS-PAGE, and molecular weight ranged from 23.5-101.0 kDa. Proteolytic activity was 0.05 to 2.08 U ml(-1), and chitinolytic activity was 46 and 449 U ml(-1) in non-inducing and induction media, respectively, after 72 hours, indicating the enzymes could increase virulence of the fungus against the insect pest.